The reason why I believe combining all of these will not be feasible is because in one of my recent conversations with Miller (and Miller please correct me if I somehow misremember here) he expressed his belief any project that exceeds N lines of code which I believe in this case it was something like 10000, it becomes unmaintainable and dies. Supposedly current pd codebase is at about 60 percent of that. That same code also lacks a lot of basic facilities like infinite undo and other core tools necessary for any kind of basic editing (given the nature of pd's structure it needs to exist inside the engine itself that is also responsible for stacking order). Features that have been added in pd-l2ork have added at least a couple of thousand lines of code with the externals and everything else obviously going well beyond that.
As a result even if we prune the code and make a libpd which again implies Miller is okay with that (as in abandoning his version and building a new GUI app that interfaces with libpd)